1. Field of the Invention
The present invention relates to dried porous crumbs of a hydrogenated block copolymer. More particularly, the present invention is concerned with dried porous crumbs of a hydrogenated block copolymer which is obtained by hydrogenating a block copolymer comprising (a) at least one polymer block composed mainly of aromatic vinyl monomer units and (b) at least one polymer block composed mainly of conjugated diene monomer units, which hydrogenated block copolymer has a molecular weight of 70,000 or more, wherein the dried porous crumbs have a water content of 1% by weight or less and have the capability of absorbing an oil in an amount of 1.0 or more, in terms of the ratio of the weight of an oil, which is absorbed by the dried porous crumbs when the dried porous crumbs are immersed in the oil at 25° C. under atmospheric pressure for 1 minute, to the weight of the dried porous crumbs. The dried porous crumbs of the present invention have not only a low water content, but also an advantageously high oil-absorbing capability, so that the dried porous crumbs can quickly absorb a satisfactory amount of a liquid additive, such as a softening agent or a silicone oil. Therefore, by using the dried porous crumbs of the present invention as a modifier when a molding resin composition is produced from a thermoplastic resin and a liquid additive, such as a softening agent or a silicone oil, a shaped article having an excellent appearance can be produced by molding. The present invention is also concerned with a method for producing, with effectiveness and efficiency, the dried porous crumbs having not only a low water content, but also an advantageously high oil-absorbing capability.
2. Prior Art
A block copolymer composed of a conjugated diene and an aromatic vinyl compound (hereinafter, the block copolymer is frequently referred to as a “conjugated diene/aromatic vinyl compound block copolymer”) has various excellent properties, and exhibits different characteristics depending on the composition thereof. Therefore, a conjugated diene/aromatic vinyl compound block copolymer is used in various application fields. For example, with respect to a conjugated diene/aromatic vinyl compound block copolymer having a relatively low content of an aromatic vinyl compound, even if the block copolymer is not vulcanized, such a block copolymer exhibits high elasticity at room temperature, which is comparable to that of a vulcanized natural rubber or a vulcanized synthetic rubber. Such a block copolymer also exhibits excellent processability at high temperature, which is comparable to that of a thermoplastic resin. Therefore, a conjugated diene/aromatic vinyl compound block copolymer having a relatively low content of an aromatic vinyl compound is widely used in various application fields, such as foot wear, modifiers for plastics, modifiers for asphalt, and adhesives. On the other hand, a conjugated diene/aromatic vinyl compound block copolymer having a relatively high content of an aromatic vinyl compound is a transparent thermoplastic resin having an excellent impact resistance, and is widely used in various application fields, such as packaging containers for food, household articles, wrapping materials for parts for household electric appliances or other industrial products, and toys. Further, a hydrogenation product of the above-mentioned block copolymer has not only the above-mentioned properties, but also excellent weathering resistance and heat resistance. Therefore, such a hydrogenation product is widely used not only in the application fields mentioned above in connection with the non-hydrogenated conjugated diene/aromatic vinyl compound block copolymer, but also in other application fields, such as automobile parts and medical equipment.
In general, the polymerization for producing a conjugated diene/aromatic vinyl compound block copolymer and the hydrogenation of the block copolymer are performed in a hydrocarbon solvent inert to a polymerization catalyst and a hydrogenation catalyst, so that each of the block copolymer and the hydrogenation product thereof is obtained in the form of a uniform solution thereof or a uniform suspension thereof in the solvent. Therefore, the obtained block copolymer and the obtained hydrogenation product need to be separated and re-covered from the solvent used. With respect to the method for separating a block copolymer or a hydrogenation product thereof from a solvent, various methods are known. As an example of such methods, there is known a method called a “steam stripping method”, which comprises adding to hot water a solution or suspension of a block copolymer or a hydrogenation product thereof in a solvent, and distilling off from the resultant mixture the solvent together with water (in the form of steam) to thereby obtain an aqueous slurry containing wet porous crumbs of a block copolymer or a hydrogenation product thereof. With respect to the steam stripping method, reference can be made to, for example, Unexamined Japanese Patent Application Laid-Open Specification No. 8-301929 (corresponding to U.S. Pat. No. 5,616,652).
For obtaining dried porous crumbs from the aqueous slurry containing the wet porous crumbs obtained by the above-mentioned method, it is necessary to remove water from the above-mentioned wet crumbs by dehydration and drying. As a method for dehydration and drying, for example, there is known a method described in Examined Japanese Patent Application Publication No. 7-13091.
The dehydration of water-containing porous crumbs is generally conducted by a mechanical compression method using a roll type or a Banbury type dehydrator, a screw extruder type compression dehydrator or the like. The drying of the water-containing porous crumbs is generally conducted by a mechanical compression method using a screw extruder type dryer, a kneader type dryer, an expander dryer or the like. Further, it is also conducted to dry the water-containing porous crumbs by a method using a hot-air dryer in combination with any one of the above-mentioned dryers used for a mechanical compression method.
The thus obtained dried porous crumbs have the capability of absorbing a liquid additive and the like and, therefore, the dried porous crumbs can be advantageously used, for example, as a modifier when a molding resin composition is produced from a thermoplastic resin and a liquid additive.
However, the above-described conventional technique for producing dried porous crumbs has a problem in that not only is the productivity low, but also the produced dried porous crumbs cannot absorb a satisfactory amount of an oil, so that even when the dried porous crumbs are used as a modifier for producing a molding resin composition from a thermoplastic resin and an additive, especially a liquid softening agent or plasticizer (e.g., an oil), it is impossible to efficiently produce a shaped article having an excellent appearance. Accordingly, it has been desired to solve the above-mentioned problem in various fields in which such additive-containing molding resin compositions are used.